Superconducting coil support structures

ABSTRACT

Support structures ( 100 ) for attaching superconducting conductors ( 106 ) to a rotor ( 50 ) of an electrical machine ( 10 ). The support structures ( 100 ) are mechanically configured to transfer loads exerted on the superconducting conductors ( 106 ) during both normal and transient operation of the rotor ( 50 ). The mechanical configuration and material of the support structures ( 100 ) further present a thermal path that is longer than the physical distance between the superconducting conductors ( 106 ) and the rotor ( 50 ) thereby minimizing heat flow from the warm rotor ( 50 ) to the cold superconducting conductors ( 106 ).

FIELD OF THE INVENTION

This invention relates in general to mechanical support structures andmore particularly to mechanical support structures for supporting asuperconducting coil of a dynamoelectric machine.

BACKGROUND OF THE INVENTION

An electric generator transforms rotational energy into electricalenergy according to generator action principles of a dynamoelectricmachine. The turning torque supplied to a rotating rotor by a combustionor steam-driven turbine is converted to alternating current (AC)electricity, typically three-phase AC, in a stationary stator thatsurrounds the rotor. The generator is a mechanically massive andelectrically complex structure, supplying output power up to 1,500 MVAat voltages up to 26 kilovolts. Electrical generators are the primarypower producers in an electrical power system.

As shown in FIG. 1, a conventional electric generator 10 comprises asubstantially cylindrical rotor 12 supporting axial field windings orrotor windings 13. A direct current (DC) supplied to the rotor windings13 produces a magnetic flux field that rotates as the rotor rotateswithin a stationary armature or stator 14. One end 15 of the rotor 12 isdrivingly coupled to a steam or gas driven turbine (not shown in FIG. 1)for providing rotational energy to turn the rotor 12. The opposing end16 is coupled to an exciter (not shown) for supplying the direct currentto the rotor windings 13. An alternating current is generated in thestationary stator windings as the rotor's magnetic flux field crossesthe stator windings. Rotor rotation subjects the rotor 12 and the rotorwindings 13 to radial centrifugal forces that may result in radialdistortion of these generator components.

The stator 14, a shell-like structure, encloses the rotor and comprisesa core 17 further comprising a plurality of thin, high-permeabilitycircumferential slotted laminations 17A placed in a side-by-sideorientation and insulated from each other to reduce eddy current losses.Stator coils are wound within the inwardly directed slots. The ACelectricity induced in the stator windings by action of the rotatingmagnetic field of the rotor 12 flows to terminals 19 mounted on thegenerator frame for connection to an external electrical load.Three-phase alternating current is produced by a generator comprisingthree independent stator windings spaced at 120° around the statorshell. Single-phase alternating current is supplied from a stator havinga single stator winding.

The rotor 12 and the stator 14 are enclosed within a frame 20. Eachrotor end comprises a bearing journal (not shown) for cooperating withbearings 30 attached to the frame 20. The rotor 12 further carries ablower 32 for forcing cooling fluid through the generator elements. Thecooling fluid is retained within the generator 10 by seals 34 locatedwhere the rotor ends penetrate the frame 20. The generator 10 furthercomprises coolers 36 receiving and cooling the cooling fluid to releasethe heat absorbed from the generator components. The cooling fluid isthen recirculated back through the generator elements.

Generator cooling system is required to remove heat energy produced byelectrical losses resulting from the large currents flowing through thegenerator conductors, including the direct current flowing through therotor windings 13 and the alternating current induced in the statorcoils. Additional heat sources include mechanical losses, such aswindage caused by the spinning rotor, and friction at the bearings 30.

In a dynamoelectric motor (including rotary motors and linear motors)the stator windings are responsive to an external electric current thatgenerates a stator magnetic field. Interaction of the stator field witha rotor magnetic field produces motion (rotary or linear) of the rotor.In an exemplary embodiment the rotor comprises a magnetically-permeablesolid material, such as an iron-core rotor, for producing the rotormagnetic field.

Copper is the material of choice for the rotor's conductive windings inboth generators and motors. Although the electrical resistance of copperis low compared to most other conductive materials, current flow throughthe copper conductors causes substantial rotor heating, diminishing themachine's power efficiency and requiring use of a cooling system tomaintain the rotor at an appropriate operating temperature.

To increase generator output and efficiency and reduce generator sizeand weight, superconducting rotor windings with effectively noresistance have been developed. These winding are commonly referred toas high-temperature superconducting (HTS) windings (distinguished fromlow temperature superconducting materials that achieve a superconductingstate at a lower temperature). It is preferred to use high-temperaturesuperconducting materials since their cooling requirements are lesssevere.

Superconductivity is a phenomenon observed in several metals and ceramicmaterials when the material is cooled to temperatures ranging from nearabsolute zero (0° K. or −273° C.) to a liquid nitrogen temperature ofabout 77° K. or −196° C. At these temperatures the metal and ceramicsexhibit effectively no electrical resistance to current flow. Thetemperature at which the material's electrical resistance issubstantially zero is referred to as the material's critical temperature(Tc). The critical temperature for aluminum is about 1.19° K. and forYBa2Cu3O7 (yttrium-barium-copper-oxide) is about 90° K. Ahigh-temperature superconducting material is maintained at or below itscritical temperature by cooling with either liquid helium or liquidnitrogen.

Since the superconducting materials exhibit substantially no electricalresistance when maintained at or below their critical temperature, thesematerials can carry a substantial electric current for a long durationwith insignificant energy losses, including losses through thegeneration of heat.

Although the HTS rotor windings (coils) exhibit little resistance tocurrent flow, they are sensitive to mechanical bending and tensilestresses that can cause premature degradation and winding failure (e.g.,an open circuit). For example, it is necessary to form bends in the HTSrotor windings that circumscribe the core. Stresses are induced at thesebends. Normal rotor torque, transient fault condition torques andtransient magnetic fields induce additional stress forces in the rotorwindings. Also, the HTS rotor winding may be subjected to over-speedforces during rotor balancing procedures at ambient temperature andoccasional over-speed conditions at superconducting temperatures duringpower generation operation. These over-speed and fault conditionssubstantially increase the centrifugal force loads on the rotor coilwindings beyond the loads experienced during normal operatingconditions. These operating conditions must be considered in the designof the HTS rotor windings and their support structures.

Normal operation of an electrical generator involves literally thousandsof start-up and shut-down cycles (i.e., cool-down cycles) over anoperational lifetime of several years. The temperature excursionsexperienced during these operating cycles can lead to winding fatigueand must therefore be considered in the design of the HTS rotorwindings.

To maintain the superconducting conductors at or below their criticaltemperature, coolant flow paths carrying coolant supplied from acryogenic cooler are disposed adjacent or proximate the windings.Typical coolants comprise liquid helium, liquid nitrogen or liquid neon.

Maintaining the structural integrity of the superconducting rotorwindings against static and dynamic loads presents a formidablechallenge to the development of a high temperature superconductinggenerator. The HTS rotor windings must be adequately supported by awinding support system to withstand the forces, stresses, strains andcyclical loads of normal and fault condition generator operationdescribed above. Moreover, the support system must ensure that thewindings do not prematurely crack, fatigue or break. Finally, the coilsupport structure must insulate the “warm” rotor (typically operating atroom temperature) from the cryogenically-cooled HTS superconductingwindings to maintain the windings at or below their criticaltemperature.

BRIEF SUMMARY OF THE INVENTION

One embodiment of the invention comprises a structure for supportingsuperconducting conductors in a spaced-apart relation from a rotor coreof an electrical machine. The structure comprises an enclosurecomprising first and second opposing sidewalls and an upper surfaceenclosing the superconducting conductors, a casing attached to the coreand comprising first and second opposing interior surfaces, theenclosure disposed within the casing, load transferring elementssupported between the enclosure and the casing for transferring loadsimposed on the superconducting conductors to the casing during operationof the electrical machine, wherein a first gap is defined in a firstthermal path between the enclosure and the casing through the elementsto impede heat flow from the rotor core to the superconductingconductors and wherein the first gap is substantially open during normaloperation of the electrical machine to lengthen the first thermal pathand tends to close during an operating transient for the electricalmachine.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be more easily understood and the advantagesand uses thereof more readily apparent when the following detaileddescription of the present invention is read in conjunction with thefigures wherein:

FIG. 1 is a cross-sectional view of a prior art electric generator;

FIG. 2 is a pictorial illustration of a rotor for use in asuperconducting dynamoelectric machine according to the teachings of thepresent invention;

FIGS. 3A, 3B, 4, 5A, 5B, 5C and 6 illustrate various views of asuperconducting coil support structure according to a first embodimentof the present invention.

FIGS. 7 and 8 illustrate various views of a superconducting coil supportstructure according to a second embodiment of the present invention.

FIGS. 9A, 9B, 10A, 10B and 11-13 illustrate various views of asuperconducting coil support structure according to a third embodimentof the present invention.

FIGS. 14-22 illustrate various views of superconducting coil supportstructure according to a fourth embodiment of the present invention.

FIG. 23 illustrates a superconducting coil support structure accordingto a fifth embodiment of the present invention.

FIGS. 24-30 illustrate various views of superconducting coil supportstructure according to a sixth embodiment of the present invention.

FIGS. 31-36 illustrate various views of superconducting coil supportstructure according to a seventh embodiment of the present invention.

In accordance with common practice, the various described features arenot drawn to scale, but are drawn to emphasize specific featuresrelevant to the invention. Like reference characters denote likeelements throughout the figures and text.

DETAILED DESCRIPTION OF THE INVENTION

Before describing in detail exemplary methods and structures forsupporting a superconducting winding (coil) in a dynamoelectric machinerotor according to the teachings of the present invention, it should beobserved that the present invention resides primarily in a novel andnon-obvious combination of elements and process steps. So as not toobscure the disclosure with details that will be readily apparent tothose skilled in the art, certain conventional elements and steps havebeen presented with lesser detail, while the drawings and thespecification describe other elements and steps pertinent tounderstanding the invention in greater detail.

The following embodiments are not intended to define limits as to thestructure or method of the invention, but only to provide exemplaryconstructions. The embodiments are permissive rather than mandatory andillustrative rather than exhaustive.

First Embodiment

Existing non-superconducting dynamoelectric machines, such as theelectric generator 10 of FIG. 1, may be retrofitted by replacing thenon-superconducting rotor 12 with a superconducting rotor 50 illustratedin FIG. 2. The superconducting rotor 50 defines alongitudinally-extending axis 52 and comprises a generallycylindrically-shaped core 54 and coaxially aligned rotor end segments 55and 57 each attached to an end surface of the core 54. A material of thecore 54 exhibits a high magnetic permeability, e.g. a ferromagneticmaterial such as iron.

The superconducting rotor 50 further comprises a generallylongitudinally-extending, racetrack-shaped superconducting coil orwinding 60 comprising generally linear axial segments 60A connected byradial segments 60B, the latter extending through openings 55A and 57Abetween end surfaces of the core 54 and the respective end segments 55and 57. In certain embodiments a vacuum shield, not shown in FIG. 2,surrounds the superconducting coil 60 and attaches to the rotor 50.

Preferably, the superconducting rotor 50 of FIG. 2 comprises a rotor ofan electric generator and the superconducting coil 60 comprises anelectric generator field (rotor) winding. One of the end segments 55 or57 includes a turbine coupling for connecting the rotor 50 to a primemover for supplying rotational energy to the superconducting rotor 50for generating electricity in the stator 14. In another embodiment, thesuperconducting rotor 50 comprises a rotor of a motor for producingrotational energy responsive to an electric field generated in asurrounding stator coil.

The end segment 57 further comprises a cryogenic transfer coupling 68.When the superconducting rotor 50 is rotating during operation of thedynamoelectric machine, the cryogenic transfer coupling 68, whichcomprises a stationary portion and a rotating portion (the individualportions not illustrated in FIG. 2), supplies cooling fluid (cryogenicfluid) from a cryogenic cooler (not shown) to closed coolant flow pathsor channels in the superconducting coil 60 to maintain thesuperconducting coil 60 at or below its critical temperature. Thecoolant flows through the coolant channels, circulates back to thecryogenic cooler where the coolant temperature is reduced and returns tothe coolant channels.

The required cooling capacity of the cryogenic cooler is directlyrelated to the heat transferred from the “warm” rotor core 54 to thesuperconducting coil 60 during operation of the superconductinggenerator. Minimizing this heat transfer by judicious design of asuperconducting coil support structure that supports the coil 60 duringnormal operation and transient conditions while minimizing heat transferreduces the required cooler capacity and the energy consumed by thecooler to cool the cryogenic fluid.

In describing the various embodiments of the invention and theirconstituent elements below, certain of the drawings and descriptive textillustrate and describe the linear axial segments 60A of thesuperconducting coil 60. It is recognized that in certain embodiments aplurality of such segments 60A are disposed in a back-to-backorientation and supported by (attached to) the core 54 to form thesuperconducting coil 60. Additionally, although illustrated anddescribed as relatively short segments herein for the purpose ofdescribing the constituent elements, the teachings of the invention canbe applied to superconducting coil segments of any length.

FIG. 3A is a cross-sectional view along a plane 3-3 of FIG. 2,illustrating a coil support structure 100 spaced apart from andsupported by the rotor core 54. FIGS. 3B and 4 further illustrate thesupport structure 100. The coil support structure 100 comprises coolantflow paths or channels 104 disposed in a bracket 105. The bracket 105 (amaterial of the bracket comprises stainless steel or Inconel®) furthersupports superconducting conductor blocks (also referred to assuperconducting blocks) 106A, 106B and 106C, each block comprising aplurality of superconducting filaments (the individual filaments are notillustrated in FIG. 3A nor in any other illustrated embodiments of thepresent invention).

In the embodiment of FIG. 3A each of the superconducting blocks 106A,106B and 106C further comprises a plurality of elongated superconductingfilament bars (formed from any of the known superconducting materials)each filament bar having a rectangular cross-sectional shape. Aplurality of such bars (13 in one embodiment) are disposed in anadjacent configuration to form each superconducting conductor block106A, 106B and 106C. Known adhesive materials and techniques areemployed to retain the filaments and the bars in the desiredconfiguration.

The elements of the coil support structure 100 support thesuperconducting conductor blocks 106A, 106B and 106C to withstand thenormal static and dynamic loads and fault condition loads, whilemaintaining the blocks 106A, 106B and 106C at or below their criticaltemperature by thermally insulating the blocks from the warm rotor core54, which typically operates at a temperature of about 350° K.

The superconducting blocks 106A, 106B and 106C are maintained at atemperature of about 30° K. by a coolant (typically liquid hydrogen)flowing through the coolant channels 104. The physical proximity of thechannels 104 to the superconducting blocks 106A, 106B and 106C asillustrated in the cross-section of FIG. 3A, provides a relativelyuniform temperature distribution along a width of each superconductingblock.

The superconducting blocks 106A, 106B and 106C (although threesuperconducting blocks are illustrated in FIG. 3A, other embodiments mayhave more or fewer than three blocks) are supported by the bracket 105along the length of the axial segments 60A (see FIG. 2). In oneembodiment the bracket 105 also supports the radial segments 60B of FIG.2. Since the coolant channels 104 are similarly supported by the bracket105, the superconducting blocks 106A, 106B and 106C are maintained at auniformly suitable temperature throughout their axial length.

The illustrated coolant flow channels 104 are elliptically shaped,however other cross-sectional shapes, such as a circle or a rectangle,are also suitable for carrying the cryogenic coolant. Other embodimentsof the present invention include more or fewer than the threeillustrated coolant flow paths.

The rotor 50, including the core 54 (see FIG. 2) and the superconductingsupport structure 100 and its constituent elements are enclosed within anon-magnetic vacuum enclosure 110 (see FIG. 3A) surrounding the rotor50. Drawing a vacuum within the enclosure 110 reduces convective heattransfer from the warm rotor core to the windings of the superconductingcoil 60. The vacuum enclosure 110 also beneficially protects thesuperconducting coil 60 and optimizes the rotor's magnetic flux.

As illustrated in FIGS. 3A and 4, the bracket 105 is supported by andspaced-apart from the core 54 by blocks 120 disposed at opposing lateraledges of the bracket 105. In one embodiment, each block 120 is rigidlyaffixed to the core 54 by a bolt 121 (typically a material of the bolt121 comprises steel or another ferrous material) extending through anopening in the block 120 and threadably engaging a threaded opening inthe core 54.

Each block 120 defines an inwardly-directed notch formed by surfaces120A, 120B, 120C and 120D (see a close-up insert of FIG. 3B) forreceiving an edge rib 105A of the bracket 105. The edge rib 105A isaxially slidable within the notch to permit axial bracket movement,relative to the affixed block 120, responsive to material contractionforces induced by coolant flow through the coolant channels 104.

Intermediate the blocks 120, the bracket 105 is supported by bolts 122(two illustrated in the exemplary embodiment of FIG. 3A) each having aradially-outward directed end affixed to the bracket 105 in a regionbetween two adjacent superconducting blocks 106 and a radially-inwarddirected end slidably supported by the core 54. In one embodiment theradially-inward directed end of each bolt 122 comprises a T-shaped head123 slidably received within a corresponding notch 54A (see FIG. 4) inthe core 54. The notch 54A extends a length of the core 54 and thus theT-shaped head 123 is freely slidable axially therein to permit motionresponsive to contraction forces induced by the coolant flow through thecoolant channels 104.

The radially-outward directed end of each bolt 122, having threadsformed thereon (the threads hidden from view in FIG. 3A), is receivedwithin a corresponding opening in the bracket 105 and is affixed theretoby threadably engaging a nut 126 to the bolt threads. Those skilled inthe art recognize that other attachment techniques and elements can beused in lieu of the various bolt/nut and threaded bolt/threaded openingattachment techniques presented in conjunction with the variousembodiments of the present invention.

As can be seen in FIG. 3A, the superconducting blocks 106A, 106B and106C are supported within the bracket 105 (and proximate the coolantchannels 104) by shoulder regions 130 of the blocks 120 and by shoulderregions 132 of the bolts 122. Other structural features for retainingthe superconducting blocks 106A, 106B and 106C within the bracket 105are known by those skilled in the art.

The physical relationship of the superconducting blocks 106A, 106B and106C relative to the other elements of the coil support structure 100allows the bracket 105 to restrain the superconducting blocks 106A, 106Band 106C against centrifugal forces produced during rotation of therotor 50. These centrifugal loads imposed on the bracket 105 and theblocks 106A, 106B and 106C are transferred to the core 54 through theblocks 120 and the bolts 122. Tangential forces (lateral forces relativeto the coil support structure 100 as illustrated in FIG. 3A), which areproduced primarily during fault conditions, are absorbed by the blocks120 and transferred to the core 54. Also, since the bracket 105 isaxially slidable within the block notches and within the core notches54A, the entire support structure 100 (except the blocks 120) is axiallyslidable relative to the core 54 to accommodate temperature-inducedcontraction of the bracket 105 (and its associated components) relativeto the warmer core.

A gap 138, see the FIG. 3B, between the surface 120D of each of the twoblocks 120 and an opposing surface 105AA of the bracket edge rib 105Apermits thermal contraction of the bracket 105 along its width due tothe cold temperatures induced by the cryogenic coolant flow through thecoolant paths 104. Since the blocks 120 are affixed to the core 54, theymaintain a temperature about equal to the rotor core temperature. Thegap 138 is also closeable responsive to fault conditions that imposelateral loads on the components of the coil support structure 100,thereby preventing damage to the superconducting blocks 106A, 106B and106C and the coolant flow channels 104.

The blocks 120 are affixed to the rotor core 54 by the bolts 121 andthus contact between the core 54 and the blocks 120 is limited to aregion proximate the bolts 121. These contact areas are minimized toreduce heat flow from the warmer core 54 through the various supportcomponents to the colder bracket 105 and the superconducting blocks106A, 106B and 106C.

The bolts 122 and blocks 120 are each formed from a material having arelatively high low-temperature strength and good thermal resistivity(i.e., a low thermal conductivity), such as a fiber-reinforced plastic(FRP) material. The FRP material resists heat flow from the warm rotorcore 54 to the cold winding components and further transfers thecentrifugal forces exerted on the winding components to the rotor core54.

Certain FRP materials exhibit a tensile strength of about 1000 Mpa andthermal conductivity of about 0.37 W/mK (watts per meterlength-temperature degree Kelvin) at 77° K. (compared to stainless steelexhibiting a thermal conductivity of about 0.6.5 W/mK). According to apreferred embodiment, a thermal barrier coating is applied to contactsurfaces of the bracket 105, the bolts 121 and 122 and the rotor core 54to further reduce heat transfer between components in physical contact.

Returning to FIG. 3A, with a vacuum drawn within the vacuum enclosure110, there is little convective heat transfer through gaps 140 or gaps138 (FIG. 3B). To reduce radiant heat transfer between the core 54 andthe superconducting blocks 106, in one embodiment reflective material isdisposed on a lower surface 142 of the blocks 106A, 106B and 106C and anopposing circumferential surface 54B of the core 54.

FIG. 4 illustrates a perspective view of a linear segment 100A of thecoil support structure 100. Individual segments can be formed in anylength such that the total number of bracket segments required totraverse the racetrack path around the core 54 (see FIG. 2) is dependenton the length of each bracket segment. In one embodiment, a singlebracket segment extends the axial length of the rotor core 54.

Irrespective of the number of bracket segments, a plurality of blocks120 are required to provide adequate support for the superconductingcoil 60. Generally, the physical attributes of the blocks 120, includingthe number employed to support the coil 60, the spacing between adjacentblocks and the distance between the block openings that receive thebolts 121 is responsive to the current capacity of the rotor 50 and theanticipated operating and fault condition loads.

According to a thermal analysis conducted by the inventors, assuming acoolant temperature of about −240° C. and a rotor core temperature ofabout 30° C., the temperature distribution within the bracket 105 isrelatively uniform due the thermal conductivity properties of thebracket material and the components supporting the superconductingblocks and the coolant flow paths. Therefore temperature gradients, andthe mechanical stresses they can create, within the bracket 105 andwithin the superconducting blocks are minimal.

In one embodiment, the heat loss for one coil support structure segment100A of FIG. 4 is about 3 watts. A total heat loss for a superconductingcoil 60 comprising about eighty segments 100A is a few hundred watts(about 260 in one embodiment), which compares favorably to a loss ofseveral hundred kilowatts in a copper rotor coil 13 (see FIG. 1) of aconventional electric generator.

The structural features of the coil support structure 100 as illustratedin FIGS. 3A, 3B and 4 provide easy serviceability of the superconductingcoil 60 and its components.

Second Embodiment

Another embodiment of a coil support structure of the present invention(illustrated in FIGS. 5A, 5B, 5C and 6) comprises a compression supportstructure 200 (see FIG. 5A) for supporting the three exemplary parallelsuperconducting blocks 106A, 106B and 106C against lateral loads(tangential loads with respect to the rotor core). The compressionsupport structure 200 comprises overhang frames 202 (constructed from amaterial having a high thermal resistance such as fiber reinforcedplastic). Base regions 202A of the overhang frames 202 extending beyondside surfaces of a conductor enclosure 212 are attached to the rotorcore 54 by any suitable fastening technique. In another embodiment thebase regions 202A are attached to a casing structure (not shown)surrounding the compression support structure 200 and attached to thecore 54. The shape of the illustrated overhang frame 202 is merelyexemplary as the shape can be optimized in response to expected normaland fault condition loads.

The support structure 200 further comprises parallel brackets 208 (fourbrackets illustrated in FIG. 5A), each bracket 208 further comprising aplurality of successive inverted V-shaped members 208A. The overhangframe 202 engages an opening formed between adjacent V-shaped members208A. In a preferred embodiment a material of the brackets 208 comprisesstainless steel.

As can be seen in FIGS. 5A and 6, a lower end 210A of an FRP (fiberglassreinforced plastic) compression block 210 is supported within an arcuatetab 211 extending from sidewalls of the conductor enclosure 212. In apreferred embodiment a material of the conductor enclosure 212 comprisesstainless steel, Inconel® or another suitable material having desiredstrength and thermal properties.

Arcuate tabs 211 also extend from the conductor enclosure 212intermediate the superconducting blocks 106A and 106B and intermediatethe superconducting blocks 106B and 106C, although these tabs are notvisible in FIG. 5A. Each of these tabs also supports a compression blockas illustrated in FIG. 6.

An upper end 210B of each FRP compression block 210 is received withinan apex region 208B of the brackets 208. The brackets 208 are affixed tothe rotor core 54 (or to a casing surrounding the compression supportstructure 200, neither shown in FIGS. 5A and 6) by any known fasteningdevice (such as by a threaded bolt passing through an opening in a lowersurface 208C of the brackets 208, the bolt engaging threads in anopening in the core 54). This arrangement causes the brackets 208 toapply a radially inwardly directed compressive bias force against theFRP elements 210 and in turn against the conductor enclosure 212 throughthe tabs 211.

As can be seen in FIG. 6, the superconducting blocks 106A, 106B and 106Care retained within separate segments of the conductor enclosure 212 byinsulated (e.g., FRP) restraining blocks 218 extending from one sidewallto an opposing sidewall along a bottom region of the conductor enclosure212. In the embodiment of FIG. 6, opposing ends of each block 218 areaffixed to opposing inside surfaces of two adjacent tabs 211. In oneembodiment the blocks 218 are affixed to the tabs 211 by passing athreaded bolt through an opening in the tab 211 for engaging threads ina mating opening of the block 218. The blocks 218 restrain thesuperconducting blocks 106A, 106B and 106C within the conductorenclosure 212 at low rotor speeds, and also maintain a proper width foreach conductor block region of the conductor enclosure 212 to avoidapplication of excessive compressive forces to sidewalls of the blocks106A, 106B or 106C.

The brackets 208 cooperate with the compression blocks 210 to supportthe normal and transient centrifugal force loads exerted on thesuperconducting blocks 106A, 106B and 106C during rotation of thesuperconducting rotor 50.

The overhang frames 202 support the centrifugal loads generated by theirown mass and also lateral loads imposed on the superconducting blocks106A, 106B and 106C during normal operation and transient conditions.These loads are transferred to the core 54 through the overhang frames202. See the close-up insets of FIGS. 5B and 5C, where an overhang frameregion 202B, defined by vertical surface 222, is snug fit within aheader opening in the conductor enclosure 212, i.e., the header openingbetween the conductor blocks 106A and 106B, a header opening between theconductor block 106B and 106C and opposing corners of the conductorenclosure 212. The snug fit is achieved by contact between the surfaces222 and surfaces 224 at the various contact locations.

Centrifugal force loads directed against the superconducting blocks106A, 106B and 106C are not transferred to the overhang frames 202 dueto gaps 229 (see FIGS. 5B and 5C) between a top surface of the conductorenclosure 212 and a facing bottom surface of the overhang frames 202;the gaps are present when the rotor is rotating at its nominal operatingspeed. The gaps also present an open in the thermal path from the warmrotor core 54 to the cold superconducting blocks 106A, 106B and 106C.

In addition to constructing the compression blocks 210 from an FRPmaterial to limit heat flow from the core 54 to the conductor blocks106A, 106B and 106C, the blocks are constructed with a desired length toincrease the thermal path length and further limit heat flow.

To permit axial contraction of the conductor enclosure 212 responsive tothe superconducting temperature of the superconducting blocks 106A, 106Band 106C, the compression blocks 210 rotate about a center point as thecurved ends 210A and 210B slide along a respective contact surface withthe arcuate tabs 211 and with the apex regions 208B.

In the embodiment of FIGS. 5A, 5B 5C and 6 the coolant flow paths areembedded within the superconducting blocks 106A, 106B and 106C and thusare not specifically illustrated in the Figures.

Third Embodiment

Another embodiment of a compression-type coil support 300 is illustratedin a perspective view of FIG. 7 and a sectional view of FIG. 8. Posts308 are fixedly attached to the core 54 (not shown) (for example,threads formed in a lower region of the posts 308 threadably engage amating threaded opening in the core 54). In conjunction with a plate 312and a nut 314 (or another fastener as known by those skilled in the art)configured as illustrated, each post 308 exerts a compressive (radiallyinwardly directed) force on the superconducting block 106 and fiberglassreinforced plastic elements 315 disposed within wells 316 in sidewallsurfaces of a conductor enclosure 318 to transfer the compressive forceexerted by the plates 312 to the conductor enclosure 316, therebycompressively biasing the conductor block 106.

Fourth Embodiment

FIGS. 9-13 illustrate yet another embodiment comprising a coil supportstructure 400 (see FIG. 9A) attached to the rotor core 54 for supportinga single superconducting block 106. Other embodiments support two ormore superconducting blocks in a side-by-side configuration employingelements similar in structure and function to the coil support structure400.

The coil support structure 400 is supported by the core 54 and disposedbetween a shear block 402 rigidly affixed to or integrally formed withthe core 54 and a removable shear block 403 disposed within a core axialslot. The shear blocks 402 and 403 restrain circumferential displacementof the support structure 400. According to one embodiment the removableshear block 403 is affixed to the core 54 by passing a bolt (not shown)through an opening in the block 403 and threadably engaging the boltinto a mating threaded hole in the core 54. To attach the supportstructure 400 to the core 54, the removable shear block 403 is removed,the structure 400 is urged against the shear block 402 and the shearblock 403 is reattached to the core 54. Attachment of the structure 400follows a reverse process.

As can be seen in the front view of FIG. 10A, the coil support structure400 comprises a channel-like conductor enclosure 406 (a preferredmaterial of the enclosure 406 comprises stainless steel) enclosing atleast three surfaces of the superconducting block 106. Cooling channels(not shown in the Figures) are embedded with the block 106.

FIG. 11 illustrates a perspective view of the conductor enclosure 406,comprising sidewall surfaces 406A and 406B (the latter hidden from viewin FIG. 11) and an upper surface 406C. Spaced apart tabs 412 extendoutwardly from a lower region of the sidewalls 406A and 406B and spacedapart tabs 413 extend upwardly from the upper surface 406C.

The conductor enclosure 406 frictionally captures (or fixedly attachesto) a lower insulation member 410 (comprising an FRP material) asillustrated. The lower insulation member 410 further comprises tabs 410Aextending laterally from the member 410 and disposed between consecutivetabs 412 extending from the sidewall surfaces 406A and 406B as can beseen in FIGS. 12 and 13. The lower insulation member 410 effectivelyforms a bottom surface to close the enclosure 406 such that thesuperconducting block 106 is restrained within the conductor enclosure406.

As illustrated in FIG. 12, a fiberglass reinforced plastic compressionblock 414 is disposed within a depression in an upper surface of eachtab 412 extending from sidewalls 406A and 406B of the conductorenclosure 406. An undulating frame 418 (formed from stainless steel inone embodiment) extends axially along the support channel 406 proximateor in contact with the sidewalls 406A and 406B. Upper curved segments418A of the undulating frame 418 an engage upper surface 414A of eachblock 414 as shown. Between adjacent tabs 412, lower curved segments418B of the frame 418 contact the laterally extending tabs 410A of thelower insulation member 410.

FIG. 13 further illustrates fiberglass reinforced plastic compressionblocks 420 captured between the lower curved segments 418B of the frame418 and an upper insulation member 428 (also formed from FRP material).The upper insulation member 428 defines a plurality of openings each onefor receiving one of the tabs 413, and further defines a plurality ofdepressions 428A proximate edge surfaces thereof for receiving uppersurfaces 420A of the FRP compression blocks 420. Lower surfaces 420B ofthe compression blocks 420 are received within the lower curved segments418B of the frame 418.

With reference to FIG. 10A, gaps 429A and 429B are defined between thesidewall surface 406A and the FRP blocks 414/420 and between thesidewall surface 406B and the FRP blocks 414/420. A gap 429C is definedbetween the upper surface 406C of the conductor enclosure 406 and alower surface of the upper insulation member 428. These gaps present ahigh thermal resistance in the various thermal paths between the warmcore and the superconducting block 106.

Returning to FIG. 9A, an external casing 432 captures the variouselements of the coil support structure 400 and is fixedly attached tothe rotor core 54 using bolts 436 threadably engaging mating threadswithin the core 54. Ribs 437 provide additional structural integrity forthe casing 432. A bottom plate 433 is attached (preferably welded) tothe casing 432.

FIG. 9A depicts only a segment of the coil support structure 400. Anextended length of the structure 400, including bolts 436 and ribs 437spaced at desired intervals, forms the linear axial segment 60A (FIG. 2)of the superconducting coil or winding 60.

To limit heat transfer from the warm rotor core to the coldsuperconducting blocks, contact between interior surfaces of theexternal casing 432 and the various support elements of thesuperconducting block 106 is limited. Only projections 428C (see FIGS.9A and 10A) of the upper insulation member 428 contact an interior uppersurface region of the external casing 432. Only the tabs 410A of thelower insulation member 410 contact an interior lower surface region ofthe external casing 432 as illustrated in FIG. 9A.

A gap 433 (see FIG. 9B) between casing interior sidewall surfaces andthe compression blocks 414 and 420 preclude contact between thesesurfaces and thus limit heat flow from the rotor 54 to thesuperconducting block 106 along this thermal path.

Heat transfer from the rotor core 54 to the superconducting block 106 isfurther impeded by the thermal insulating properties of the upper andlower insulation members 428 and 410 and the compression blocks 414 and420, all formed from a material having a high thermal resistance, suchas an FRP material.

In addition to limiting heat flow to the superconducting block 106, theelements of the coil support structure 400 also limit loads (e.g.centrifugal, lateral and axial) imposed on the conductor block 106 bynormal operation and fault conditions of the superconducting generator.

When the rotor of the superconducting generator is rotating atrelatively low speeds (e.g. a turning gear speed), movement of thesuperconducting block 106 due to its weight is restrained by the lowerinsulation member 410.

Higher speed centrifugal loads on the block 106 and the enclosure 406are transferred by the tabs 412 to the fiberglass reinforced plasticcompression blocks 414 then to the fiberglass reinforced plasticcompression blocks 420 through the frame 418. The frame 418 isconstructed from stainless steel and thus displays some elasticityduring transfer of the load between the compression blocks 414 and 420.From the compression blocks 420, the load is transferred to the upperinsulation member 428 then to the external casing 432 along theprojections 428C (see FIG. 10A) in contact with an interior surface ofthe external casing 432. See also FIG. 9A.

As can be seen in FIG. 13, a plurality of gaps 428B are formed in theupper insulation member 428 for defining thermal conductive pathstherein. The illustrated shape and location of the gaps 428B are merelyexemplary. In one embodiment, a gap width is about 1-2 mm at thegenerator's rated speed. The gaps close responsive to fault or transientconditions that impose additional loads on the elements of the coilsupport structure 400.

The gaps 428B are configured and located to create a sufficiently longthermal conductive path for heat flow from the warm rotor through theexternal casing 432 to the projections 428C (see FIG. 10A) of the upperinsulation member 428, through the path in the insulation member 428 asdefined by the gaps 428B to the “cold” tabs 413 extending from thecasing 406 to the superconducting block 106. Lengthening this heat flowpath helps to maintain the cold temperature of the superconductingconductors 106. One such path is identified by arrowhead 428C in FIG.13.

When the lateral load is relatively small during normal operation, thecross-sectional stiffness of upper insulation member 428 is sufficientto resist closure of the gaps 428B and thus the heat path through theupper insulation member 428 is maintained as described above. Thesuperconducting block 106 is retained in place against normal lateralloads by the upper and lower insulation members 428 and 410, which alsoserve to damp rotor vibrations.

Under fault conditions the lateral loads (that is, loads in directionsrepresented by a double arrowhead 440 in FIG. 13) increase, deformingthe upper insulation member 428 and reducing the gap width (undercertain fault conditions the gaps 428B may close). Under such conditionsthe lateral loads imposed on the superconducting block 106 aretransferred to the casing 432, via the upper insulation member 228,preventing deformation of the superconducting filaments within the block106.

Since the duration of a transient or fault condition is typically a fewseconds closure of the gaps 428B and the resulting shorting of thethermal path between the conductors 106 and the rotor core 54 does notresult in an appreciable temperature change the superconductingconductors in the block 106. When the loading returns to a steady statecondition after the fault, the gap width is restored and the thermalpath returns to its extended state.

The ribs 437 (see FIG. 9A) of the external casing 432 provide supportfor both centrifugal and lateral loads encountered by thesuperconducting block 106 (and their associated components) duringnormal generator operation and during fault conditions.

The fiberglass reinforced plastic compression blocks 414 and 420 areoriented to adapt to the axial thermally-induced contraction of the coilsupport structure 400 at the low operating temperatures required tomaintain the superconducting block 106 in a superconducting state. Thatis, the significant temperature differential between the rotor core 54and the coil support structures 400 causes the latter to contractrelative to the former. To accommodate this contraction, the curvedsurfaces 414A/414B and 420A/420B of the compression blocks 414 and 420(see FIG. 13) allow the blocks to rotate (in a plane parallel to thesidewall surfaces 406A and 406B) so that the cold superconducting block106 can move axially relative to the external casing 432, which isattached to the rotor core. The upper and lower insulation members 428and 410 also move relative to the external casing 432 as the enclosure406 contracts.

The degree of rotation for an y block 414 or 420 depends on the axiallocation of the block relative to the axial length of the rotor 54, witha rotation angle of about zero degrees at a midpoint of the rotor's axisand a maximum rotation angle at the rotor ends.

Preferably a vacuum enclosure (such as the vacuum enclosure 110 of FIG.3A) surrounds the rotor core 54 and the components associated with thecoil support structure 400. A vacuum drawn around the structure 400reduces convective heat transfer from the warm rotor core 54 to thewindings of the superconducting block 106. The vacuum enclosure alsoreduces the intrusion of stray magnetic fields into the regionsurrounding the rotor core 54.

Fifth Embodiment

FIG. 14 depicts an elevation view and FIG. 15 a perspective view of onesegment of a tension-only coil support structure 500 according toanother embodiment of the present invention.

As illustrated in FIG. 14, the single superconducting block 106 (andcoolant channels for carrying the cryogenic coolant embeddedtherewithin) is supported by a conductor enclosure 504 (preferablyconstructed from stainless steel) comprising rib supports 508 (see FIG.16) disposed on an upper surface 510 and further comprising sidewallsurfaces 514 and 516 (see FIG. 16). Although this embodiment isdescribed and illustrated with a single superconducting block 106, otherembodiments comprising two or more superconducting blocks 106 are easilyaccommodated, as can be appreciated by those skilled in the art.

A lower insulation member 518 is disposed to form a lower surface of theconductor enclosure 504, enclosing the superconducting block 106 withinthe enclosure 504. See FIG. 16. As illustrated in FIG. 18, the lowerinsulation member 518 defines notches 522 for receiving tabs 526protruding downwardly from the sidewall surface 514 and 516 (see FIG.16) of the enclosure 504. Preferably, bolts 528 or other attachmentdevices extend through an opening in the tabs 526 for engaging matingthreaded holes in the region of the notches 522 in the lower insulationmember 518 to attach the lower insulation member 518 to the conductorenclosure 504. (The lower insulation member 410 of FIG. 10 is similarlyaffixed to the conductor enclosure 406.) This arrangement can exertsufficient restraining forces on the superconducting block 106 torestrain the block within the enclosure 504 against its own weight andagainst forces exerted on the block 106 at relatively low rotor speeds.

As can be seen in FIG. 17, after assembly of the coil support structure500, fingers 530 extending laterally from the lower insulation member518 are received within notches 534 in a lower region of an externalcasing 536.

The lower insulation member 518 defines gaps 518A (see FIGS. 17 and 18)for establishing a thermal conductive path through the insulation member518. In one embodiment the gaps are about two to five millimeters wide.One such path is illustrated by an arrowhead 518B. The illustrated shapeand location of the gaps 518A are merely exemplary and therefore theillustrated path 518B is merely exemplary. Since little heat flowsacross the gaps, they lengthen the thermally conductive path from thewarm rotor core 54 through the external casing 536 attached to the core,to the fingers 530 of the lower insulation member 518 in contact withthe superconducting block 106. See FIG. 17. Lengthening this heat flowpath through use of the gaps helps to maintain the cold temperature ofthe superconducting block 106. However in response to certain loadconditions experienced by the coil support structure 500, the gaps closeto direct the load forces to structural elements capable of absorbingthem (i.e., the rotor core 54).

As further illustrated in FIG. 18, the fingers 530 extending from thelower insulation member 530 extend downwardly from a plane of the lowerinsulation member 518, creating a gap 537 (see FIG. 14) between a lowersurface of the superconducting block 106 and an upper surface of thefingers 530, further limiting heat flow from the warm rotor core 54 tothe superconducting block 106. In a preferred embodiment the gap isabout 3 to 5 mm. The area in which the gap is formed can also be seen inFIG. 18, illustrating an inclined surface 518C extending downwardly froman upper surface 518D of the lower insulation member.

To properly limit the forces imposed on the superconducting filamentswithin the block 106, it is desired to increase the thickness of thelower insulation member 518. However, an increased thickness reduces thethermal path resistivity, i.e., an increased thickness increases thecross section of the thermal path, which reduces the thermal pathresistance. Reduction of the thermal path resistance allows more heatflow from the warm rotor to the cold superconducting conductors. Thusthe trade off between maintaining the structural integrity of thesuperconducting conductors by limiting forces imposed on them anddecreasing the thermal resistance of those structures must beconsidered.

As illustrated in FIG. 19, an upper arcuate segment 540A of each tensionfiberglass reinforced plastic (FRP) band 540 encircles a rib support 508and extends toward the lower insulation member 518. A protruding member544A of a support leg 544 (wedge-shaped or T-head shaped and preferablycomprising a ferrous material) is captured within a lower arcuate region540B of each band 540, while a body portion 544B is received withinnotches 546 (see FIG. 17) of the external casing 536. The bands 540transfer centrifugal loads imposed on the enclosure 504 (and thesuperconducting block 106 disposed therein) to the casing 536 throughthe support legs 544. Note that an upper surface 544C of the support leg544 contacts a surface 546A of the notch 546 to transfer the centrifugalloads from the support leg 544 to the casing 536. These loads are thentransferred to the core 54 through the casing 536.

The upper and lower arcuate segments 540A and 540B of the FRP bands 540permit the bands 540 to adapt to the axial contraction induced by thecold components of the tension-only support structure 500. As thechannel 504 contracts axially due to coolant flow through coolantchannels embedded within the superconducting block 106, the support legs544 are held firmly within the notches 546 of the casing 536. But theupper arcuate segments 540A are permitted to slide freely over the ribsupports 508 and the lower arcuate segments 540B are permitted to slidefreely over the protrusions 544B to allow axial contraction of thechannel 504 (and the superconducting block 106). This motion preventsdamage to the superconducting conductors and the conductor enclosure504.

FIG. 21 illustrates elongated insulation members 554 disposed betweenadjacent bands 540. Insulation members 558 (illustrated in FIGS. 14 and15) are received within openings 562 (see FIG. 20) of the externalcasing 536 and mate with notches disposed at opposing ends of theelongated insulation members 554 as illustrated in FIGS. 14, 15, 21 and22. FIG. 22 also illustrates gaps 558A in the insulation member 558 forlengthening the thermal path within the member 558.

The insulation members 554 and 558 cooperate to support lateral loadsimposed on the superconducting block 106 by transferring these loads tothe external casing 536. The members 554 and 558 also damp rotorvibrations and insulate the cold superconducting block 106 from thesurrounding warm components, in particular the external casing 536. Asfurther illustrated in FIG. 14, a gap 559 is defined between a region ofan outwardly facing surface of the insulation member 558 and an inwardlyfacing surface of the notches 562. Under certain transient conditions,the gap 559 closes to transfer lateral forces to the external casing536.

A bottom plate 566 (see FIG. 14) is affixed (preferably by welding) tothe external casing 536 to completely enclose the structural elementstherewithin and permit drawing a vacuum within the external casing 536.

The tension-only coil support structure 500 is disposed on the rotorcore 54 with a sidewall 536A of the casing 536 urged against the shearblock 402 as illustrated in FIG. 14. The casing 536 is rigidly affixedto the rotor core 54, typically by engaging bolts 570 (see FIG. 15) intothreaded receiving holes formed in the core 54. The removable shearblock 403 is urged against a sidewall 536B of the casing 536 and rigidlyaffixed to the core 54 (typically by bolting to the rotor core 54).

A vacuum/magnetic shield 578 (see FIG. 14) permits drawing a vacuumsurrounding the casing 536 to limit convective heat transfer.

Sixth Embodiment

FIG. 23 illustrates a conductor support structure 598, similar to theconductor support structure 500, but suitably sized to accommodate twosuperconducting conductors 106A and 106B.

Seventh Embodiment

According to another embodiment of the present invention a tension-onlycoil support structure 600 supports two superconducting blocks 106A and106B, although more or fewer superconducting blocks can be accommodated.The coil support 600 is illustrated in an elevation view of FIG. 24 anda perspective view of FIG. 25, and elements thereof are illustrated inFIGS. 26-30.

The dual superconducting blocks 106A and 106B are supported within adual conductor block enclosure 604. The dual conductor enclosure 604,preferably constructed from stainless steel, comprises sidewall surfaces604A and 604B and an interior wall surface 604C separating thesuperconducting blocks 106A and 106B, which are omitted from FIG. 26 forclarity. A cross beam 606 extends from an upper surface 604D of theenclosure 604; rib supports 608 protrude laterally from the cross beam606.

With reference to FIGS. 26 and 27, a lower insulation member 610 forms abottom surface for the enclosure 604 to retain the superconductingblocks 106A and 106B within the enclosure 604. Notches 612 defined inthe lower insulation member 610 (see FIG. 27) engage tabs 616 (see FIG.26) protruding downwardly from the sidewall surfaces 604A and 604B ofthe enclosure 604. Note that the tabs 616 protruding downwardly from thesidewall surface 604B are hidden from view in FIG. 26. Each tab 616 isheld within a respective notch 612 by a bolt (or other fasteningmechanism) extending through an opening in each tab 616 for threadablymating with threads formed in an opening within the lower insulationmember 610.

As can be further seen in the bottom view of FIG. 28, fingers 620extending laterally from the lower insulation member 610 engage notches622 in a lower region of an external casing 626. As can be seen in thevarious Figures, fingers 620 disposed on the outer edges of the lowerinsulation member 610 are narrower than those disposed in a mid regionof the lower insulation member 610. When a plurality of the coil supportstructures 600 are placed in an end-to-end arrangement to form the coilsupport structure 60 of FIG. 2, two lower insulation members areabutted, thereby doubling the width of the fingers 620 on the outeredges of the lower insulation member 610.

As illustrated in FIG. 29, the tension fiberglass reinforced plastic(FRP) bands 540 each comprise the upper arcuate segment 540A partiallyencircling the rib supports 608 and the lower arcuate segment 540Bcaptured by protruding members extending from support legs 544. A bodyportion of each support leg 544 is captured within openings 630 (seeFIG. 28) of the external casing 626. FIGS. 24 and 25 also illustrate thesupport legs 544 captured within the openings 630 of the casing 626.

The band elements 540 transfer centrifugal loads imposed on theenclosure 604 and the superconducting blocks 106A and 106B disposedtherein, to the casing 536 through the support legs 544. Attachment ofthe casing 536 to the core 54 as illustrated in FIG. 24 transfers theseloads to the core 54.

The upper arcuate segments 540A of the FRP band elements 540 permit theband elements 540 to adapt to the axial contraction induced by the coldcomponents of the tension-only support structure 600 as the upperarcuate segments 540A slide along the rib supports 608 and the lowerarcuate segments 540B slide along protrusions 544B responsive to axialcontraction of the enclosure 604 and the superconducting conductors 106Aand 106B disposed therein.

FIG. 29 also illustrates elongated insulation members 554 disposedbetween adjacent band elements 540 and received within openings 644 (seeFIG. 26) between successive cross beams 606. Ends 554A and 554B of theinsulation members 554 each engage the insulation member 558 asillustrated in FIGS. 29 and 22. When the casing 626 is disposed over thesupport components, as illustrated in FIGS. 24 and 25, the insulationmembers 558 are disposed within opposing notches 626A and 626B (see FIG.30) of the casing 626.

The insulation members 554 and 558 cooperate to support lateral loadsimposed on the superconducting conductors 106A and 106B, damp rotorvibrations and insulate the cold superconducting blocks 106A and 106Bfrom the surrounding warm components.

The lower insulation member 610 and the insulation members 558 definegaps therein (respectively gaps 610A illustrated in FIG. 27 and gaps558A illustrated in FIG. 29) to elongate the thermal conductive pathsbetween the warm rotor and the cold enclosure 604 and thesuperconducting blocks 106A and 106B disposed therein. As can be seen inFIGS. 26 and 27, the cold enclosure 604 contacts the lower insulationmember 610 where the tabs 616 are received within the notches 612. Thethermal path continues through the lower insulation member 610 alongpaths defined by the gaps 610A. The paths extend to the fingers 620 thatmate with the notches 622 of the casing 626 then to the core 54.

A bottom plate 644 (see FIG. 24) is affixed (typically be welding) tothe external casing 626 to completely enclose the structural elementswithin the external casing 626.

The tension-only coil support structure 600 is disposed on the rotorcore 54, as illustrated in FIG. 23, preferably using threaded bolts (notshown) passing through casing openings 626C (see FIG. 30) and engagingmated threaded openings in the core 54. Further the casing is rigidlycaptured between the integral shear block 402 and the removable shearblock 403.

The shield 110 (see FIG. 24) is disposed surrounding the core 54 and thesupport structure 600 as in the embodiments described above, permittinga vacuum to be drawn to limit convective heat transfer between thevarious elements of the coil support structure 600.

Eighth Embodiment

Another embodiment of a compression-type coil support 700 for supportingtwo superconducting blocks 106A and 106B is illustrated in a perspectiveview of FIG. 31A. In other embodiments more or fewer superconductingblocks can be supported. The support structure 700 comprises a dualsupport channel 706 (a preferred material of the support channel 706comprises stainless steel) for surrounding at least three surfaces ofthe superconducting blocks 106A and 106B. FIG. 31A depicts a region ofthe elongated coil support structure 700 that forms the superconductingcoil 60 of FIG. 2. Within the superconducting coil 60, the bolts 436 andexternal ribs 736 are disposed at predetermined intervals along anextended coil support structure 700. The coolant channels are embeddedwithin the superconducting blocks 106A and 106B.

FIG. 32 illustrates a perspective view of a first embodiment of the dualsupport channel 706 including a cross member 710 extending from a topsurface 706A and tabs 712 having an arcuate depression 712A in an uppersurface thereof extending from sidewall surfaces 706B and 706C of thesupport channel 706. The arcuate tab 712 on the right-hand sidewall isnot visible in FIG. 32.

FIG. 33 illustrates a perspective view of a second embodiment of a dualsupport channel 715 including grooves 716 formed in a top surface 715Aand operative as coolant channels for carrying the coolant proximate thesuperconducting blocks 106A and 106B.

Tabs 718 extend upwardly from the cross member 710 in both supportchannel embodiments 706 and 715.

The support channels 706 and 715 are interchangeable within the scope ofthe present invention, but for simplicity subsequent references willrefer only to the support channel 715.

The support channel 715 overlies a lower insulation member 720 asillustrated in FIG. 34, with the superconducting blocks 106A and 106Bomitted for clarity. As illustrated, a lower region of each tab 712 isreceived within a notch 720A in the lower insulation member 720, thenotch formed between two successive extending fingers 724. The lowerinsulation member 720 is attached to the support channel 715 by, forexample, a threaded bolt (not shown) passing through an opening in eachtab 712 into a mating threaded opening in the lower insulation member720. Thus the lower insulation member forms a bottom surface of thesupport channel 715 to secure the superconducting blocks 106A and 106Bwithin the support channel 715.

As illustrated in FIG. 35 a lower region 414A of the fiberglassreinforced plastic compression block 414 is supported within the arcuateupper surface 712A (see FIG. 34) of each tab 712. Only the left-side tab712 and the corresponding compression block 414 are visible in FIG. 35.

The undulating frame 418 extends adjacent the left and right sidewalls715B and 715C of the dual support channel 715 proximate or in contactwith therewith. The upper arcuate segments 418A of the undulating frame418 engage upper regions 414B of each compression block 414. The lowerarcuate segments 418B of the frame 418 are received within arcuatedepressions 724A in the laterally extending fingers 724 of the lowerinsulation member 720, as illustrated in FIGS. 35 and 36.

As further illustrated in FIGS. 35 and 36, the fiberglass reinforcedplastic compression blocks 420 are captured between the lower curvedsegments 418B of the frame 418 and an upper insulation member 728. Theupper insulation member 728 defines a plurality of recesses 728A in anunderside surface and proximate lateral edge surfaces thereof forreceiving the upper regions 420A of each compression block 420. Theupper insulation member 728 also defines an opening therein forreceiving the tab 718 as illustrated.

As illustrated in FIG. 31B a thermally insulating gap 742 is presentbetween outer-facing sidewalls of the compression blocks 420 (and 414)and a proximate inside surface of the external casing 732.

Returning to FIG. 31A, an external casing 732 captures the elements ofthe coil support structure 700 and is fixedly attached to the rotor core54 using bolts 436 for threadably engaging mating threads within thecore 54.

Only the upper and lower insulation members 728 and 720 contactrespective interior upper and lower surface regions of the externalcasing 732. The upper and lower insulation members 728 and 720 definerespective gaps 728B and 720B (see FIGS. 34 and 36) (in one embodimenteach gap having a width of about 2 to 5 mm) for determining thermalconductive paths therein. The illustrated shape and location of the gaps728B and 7208B are merely exemplary. The gaps are configured to create asufficiently long thermal conductive path for heat flow from the warmrotor core 54 through the external casing 732 to the upper and lowerinsulation members 720 and 728 in contact with the casing 732.Lengthening this heat flow path helps to maintain the cold temperatureof the superconducting blocks 106A and 106B.

When the rotor of the superconducting generator is stopped or rotatingat relatively low speeds (e.g. a turning gear speed), thesuperconducting blocks 106A and 106B are restrained within the supportchannel 715 by the lower insulation member 720. At operating high speedsthe centrifugal loads exerted on the blocks 106A and 106B aretransferred by the tabs 712 extending from the support channel sidewallsurfaces 715B and 715C to the compression blocks 414 then to thecompression blocks 420 through the frame 418. From the compressionblocks 420 the load is transferred to the upper insulation member 728 tothe external casing 732. Note that only peripheral regions 728C (seeFIG. 36) contact interior surfaces of the casing 732.

Heat transfer from the rotor core 54 to the superconducting blocks 106Aand 106B is impeded by the thermal insulating properties of the upperand lower insulation members 720 and 728, typically formed from an FRPmaterial, and the gaps 720B and 728B formed therein.

The external ribs 736 (see FIG. 31A) of the external casing 732 providesupport for both centrifugal and lateral loads imposed on the coilsupport structure 700 during operation and during fault conditions. Abottom plate 738 (see FIG. 31A) is affixed to a bottom surface of theexternal casing 732.

The fiberglass reinforced plastic compression blocks 414 and 420 areconstructed to adapt to the thermal contraction of the support channel715 at the low operating temperatures required to maintain thesuperconducting coils 106A and 106B in a superconducting state. Thecurved ends 414A/414B and 420A/420B of the blocks 414 and 420 (see FIGS.35 and 36) allow the blocks to rotate about a block center, causing thecurved ends 420B and 414A to slide along the respective lower and upperarcuate segments 418B and 418A of the frame 418, and the curved ends420A and 414B to slide along the recesses 728A and 712A (see FIG. 34) sothat the support channel 715 (including the superconducting blocks 106Aand 106B therein) can contract axially relative to the fixed warm rotorcore 54. The upper and lower insulation members 720 and 728 can alsomove axially relative to the rotor core 54 in response to contractionforces. The degree of rotation depends on the axial location of theblocks 414 and 420 on the rotor core 54, with a rotation angle of aboutzero degrees at a midpoint of the rotor's axis, with a maximum rotationangle at the rotor ends.

As in the embodiments described above, the casing 732 is rigidlyrestrained circumferentially on the core 54 between the affixed shearblock and the removable shear block. A vacuum/magnetic shield 578 (seeFIG. 14) surrounds the coil support structure 700 for drawing a vacuumwithin the shield 578.

The various described embodiments of the invention comprise componentsconstructed from materials having a desired thermal resistance andmechanical configuration to support the superconducting conductorsduring operation of the electrical machine. During normal operation alength of the various thermal paths between the cold superconductingconductors and the warm rotor core are substantially maximized to limitheat flow along the path and thereby minimize conductor temperatureincreases. During transient conditions that can impose undesiredmechanical loads on the conductors the thermal paths are altered (e.g.,the path length is shortened as gaps between and within components tendto close) by these transient forces. Altering the thermal paths improvestransference of the transient forces away from the conductors to therotor core, at the expense of lowering the thermal resistance in thethermal paths during the transient event. Once the transient conditionhas subsided, the thermal paths return to their normal condition and thethermal resistance of the paths increases. Thus the thermal paths areformed to present a longer path for heat flow than the physical distancebetween the superconductors and the rotor, but the paths are shortened(e.g., gaps within the paths are closed) responsive to certain loads toprovide additional load bearing and load transferring capabilities asrequired.

The components of the embodiments described in conjunction with FIGS.9-13 and 31-36 impose compressive forces on the superconductingconductors to transfer the normal and transient forces to the rotor corevia the casing affixed to the core and surrounding the conductors. Theembodiments described in conjunction with FIGS. 14-22, 23 and 24-30impose tension forces on the superconducting conductors, transferringthe normal and transient forces to the casing and then to the core.

The mechanical components of each embodiment also permit movement of thesuperconducting conductors and proximate components relative to therotor core, while maintaining structural integrity during both normaland transient operation. As the coolant lowers the conductor temperaturethe conductors and proximate components tend to contract relative to thewarmer rotor. Thus movement responsive to the contractive forces isnecessary to prevent conductor damage.

While the present invention has been described with reference topreferred embodiments, it will be understood by those skilled in the artthat various changes may be made and equivalent elements may besubstituted for the elements thereof without departing from the scope ofthe invention. The scope of the present invention further includes anycombination of elements from the various embodiments set forth herein.In addition, modifications may be made to adapt a particular situationto the teachings of the present invention without departing from itsessential scope. Therefore, it is intended that the invention not belimited to the particular embodiments disclosed, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. A structure for supporting superconducting conductors in aspaced-apart relation from a rotor core of an electrical machine,comprising: an enclosure comprising first and second opposing sidewallsand an upper surface enclosing the superconducting conductors; a casingattached to the core and comprising first and second opposing interiorsurfaces, the enclosure disposed within the casing; load transferringelements supported between the enclosure and the casing for transferringloads imposed on the superconducting conductors to the casing duringoperation of the electrical machine, wherein a first gap is defined in afirst thermal path between the enclosure and the casing through theelements to impede heat flow from the rotor core to the superconductingconductors; and wherein the first gap is substantially open duringnormal operation of the electrical machine to lengthen the first thermalpath and tends to close during an operating transient for the electricalmachine.
 2. The structure of claim 1 further comprising a lowerinsulation member forming a lower surface of the enclosure forsupporting the superconducting conductors within the enclosure, regionsof the lower insulation member in contact with the superconductingconductors and other regions in contact with the casing, the lowerinsulation member defining second gaps therein that define a secondthermal path from the casing through the lower insulation member to thesuperconducting conductors, and wherein the second gaps are in an openstate during normal operation of the electrical machine and tend towarda closed state during operating conditions that impose above-normalforces on the superconducting conductors, the second thermal path havinga length greater than a distance between the conductors and the casing.3. The structure of claim 1 wherein the regions in contact with thecasing comprise fingers extending from sidewall surfaces of the lowerinsulation member and received within openings defined in the casing. 4.The structure of claim 1 wherein in response to contractive forcesimposed on the enclosure the elements permit movement of the enclosurerelative to the casing.
 5. The structure of claim 1 further comprisingan upper insulation member having regions in contact with an upperinterior surface of the casing and other regions in contact with theupper surface of the enclosure, the upper insulation member definingsecond gaps therein that define a second thermal path through the upperinsulation member between the casing and the enclosure, wherein thesecond gaps are in an open state during normal operation of theelectrical machine and tend toward a closed state during operatingconditions that impose above-normal forces on the superconductingconductors, and wherein the second thermal path has a length greaterthan a distance between the conductors and the casing.
 6. The structureof claim 1 wherein the elements comprise a plurality of firstcompression blocks disposed proximate the first sidewall and a pluralityof second compression blocks disposed proximate the second sidewall fortransferring the loads from the enclosure to the casing.
 7. Thestructure of claim 1 wherein the elements comprise a plurality of firsttension bands disposed proximate the first sidewall and a plurality ofsecond tension bands disposed proximate the second sidewall, each of thefirst and the second tension bands comprising an upper arcuate segmentsupported by the enclosure and a lower arcuate segment supported by thecasing.
 8. The structure of claim 1 wherein a material of the elementspresents a thermal conductivity less than about 0.37 W/mK at about 77°K.
 9. The structure of claim 1 wherein the casing comprises a closedstructure for drawing a vacuum therein.
 10. The structure of claim 1wherein the electrical machine comprises an electric generator.
 11. Astructure for supporting a superconducting conductors in a spaced apartrelation from a rotor core of an electrical machine, wherein coolantchannels are disposed proximate the conductors, the structurecomprising: a casing attached to the rotor core defining a plurality ofnotches in an interior surface in-a lower region of the casing andfurther defining an axial cavity in an interior surface in an upperregion of the casing; an elongated enclosure defining a channel boundedby an upper surface and spaced apart first and second sidewallsextending therefrom, the conductors disposed within the channel and theelongated enclosure disposed within the casing, a plurality of ribsupports extending beyond the first and the second sidewalls; a lowerinsulation member forming a bottom surface of the elongated enclosureand comprising fingers extending from opposing edges of the lowerinsulation member, each finger received within one of the notches, thelower insulation member defining first gaps therein for defining athermal path within the lower insulation member; projections extendingfrom the interior surface of the casing; band members each comprising anarcuate segment at a first end encircling a portion of one of the ribsupports and an arcuate segment at a second end encircling a portion ofone of the projections; a plurality of first insulation members eachdisposed between adjacent rib supports, each first insulation membercomprising a first and a second end; and a plurality of secondinsulation members supported at each end of each one of the plurality offirst insulation members, each one of the second insulation membersreceived within the axial cavity, a second gap defined between anoutward surface of the second insulation member and a inward surface ofthe cavity.
 12. The structure of claim 11 defining a gap between anupper interior surface of the casing and the first insulation member.13. The structure of claim 11 wherein the arcuate segment at the firstend of each band member slides along the rib supports and the arcuatesegment at the second end of each band member slides along theprojections as the elongated enclosure contracts responsive to atemperature of the conductors, and wherein the lower insulation memberis attached to the elongated enclosure and moves relative to the casingas the elongated enclosure contracts responsive to the temperature ofthe conductors.
 14. The structure of claim 11 wherein the lowerinsulation member defines a plurality of third gaps therein, wherein thethird gaps are in a open state during normal operation of the electricalmachine and tend toward a closed state responsive to loads exerted onthe structure during a transient condition of the electrical machine,wherein in the open state the gaps define longer thermal paths betweenthe casing and the elongated enclosure than in the closed state.
 15. Thestructure of claim 11 wherein a material of the band members, the lowerinsulation member, and the first and second insulation members comprisesfiber reinforced plastic having a thermal conductivity of less thanabout 0.37 W/mK at about 77° K.
 16. The structure of claim 11 whereineach one of the plurality of second insulation members defines aplurality of third gaps therein, wherein the third gaps are in a openstate during normal operation of the electrical machine and tend towarda closed state responsive to loads exerted on the structure during atransient condition of the electrical machine, wherein in the open statethe gaps define longer thermal paths between the casing and the firstinsulation member than in the closed state.
 17. The structure of claim11 wherein the elongated enclosure defines a first channel for receivinga first plurality of superconducting conductors and a second channel forreceiving a second plurality of superconducting conductors.
 18. Thestructure of claim 11 wherein the rib supports extend laterally from across beam extending upwardly from the upper surface.